gpio: omap: remove remainder of list management

Commit c4791bc6 ("gpio: omap: drop omap_gpio_list") removed the
list head and addition to the list head of each gpio bank, but failed
to remove the list_del() call and the node inside struct gpio_bank.
Remove these too.

Fixes: c4791bc6 ("gpio: omap: drop omap_gpio_list")
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>